Objective: To elucidate for the first time the phenological stage effect on polyphenol, flavonoid and proanthocyanidin contents of pennyroyal (Mentha pulegium) as well as their antioxidant capacities and insecticidal potentials against Tribolium castaneum and Lasioderma serricorne. Methods: Crude methanol extracts from pennyroyal (Mentha pulegium) aerial parts were evaluated for their antiradical, reducing power activities and repellent potentials against selected coleopteran insects during different phenological stages. Results: Phenolic contents of pennyroyal aerial parts and their antioxidant effects were significantly dependent on maturity stage of the plant. The maximum of phenol production was reached during the full flowering stage. Apigenin was the major phenol in Mentha pulegium with an amount of 6.01 mg/g of dry vegetable matter during this period. Nevertheless, at fructification stage, the highest antioxidant activity was not related to high phenolic content. The repulsive effect of pennyroyal extract showed that Lasioderma serricorne was more susceptible to pennyroyal extract than Tribolium castaneum with corresponding median repellent dose values of 0.124 and 0.006 mg/mL respectively. Moreover, great differences in insect repulsion depending on extract concentrations, exposure time and developmental stage was observed. For the lowest concentration (0.125 mg/mL), the repellent effect against Tribolium reached its maximum (90%) during the fructification stage (after 24 h of exposure) while this repellent effect was 80% during the vegetative stage. Conclusions: Due to the strong insecticidal potential of pennyroyal extracts, this study highlights the therapeutic properties of this plant and encourages its use as a safer, environmental-friendly and efficient insecticide in food industry.